From 9cbc5bd32318e4d2d6df7551cb07a6d48773bbf4 Mon Sep 17 00:00:00 2001
From: Warner Losh <imp@FreeBSD.org>
Date: Sun, 18 Jun 2017 21:03:35 +0000
Subject: [PATCH] Load the transmit dma buffer at attach time as well. We don't
 need to load and unload it all the time since the buffer never changes. In
 addition, we were loading it with a hardware spin lock held, which makes the
 sleepable lock in busdma (for the bounce pages) trigger a witness warning, as
 well as ipend being called with it held by uart, which made it impossible to
 unload.

These differences don't matter with the v4 busdma implementation, but
they do with the v6 implementation since the latter likes to bounce
transactions more, and will always do so for Atmel's driver.

It's more efficient as well as being more correct.
---
 sys/arm/at91/uart_dev_at91usart.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/sys/arm/at91/uart_dev_at91usart.c b/sys/arm/at91/uart_dev_at91usart.c
index cac5e6a2abd9..4065db33040c 100644
--- a/sys/arm/at91/uart_dev_at91usart.c
+++ b/sys/arm/at91/uart_dev_at91usart.c
@@ -72,6 +72,7 @@ struct at91_usart_softc {
 	struct uart_softc base;
 	bus_dma_tag_t tx_tag;
 	bus_dmamap_t tx_map;
+	bus_addr_t tx_paddr;
 	uint32_t flags;
 #define	HAS_TIMEOUT		0x1
 #define	USE_RTS0_WORKAROUND	0x2
@@ -472,6 +473,9 @@ at91_usart_bus_attach(struct uart_softc *sc)
 	err = bus_dmamap_create(atsc->tx_tag, 0, &atsc->tx_map);
 	if (err != 0)
 		goto errout;
+	if (bus_dmamap_load(atsc->tx_tag, atsc->tx_map, sc->sc_txbuf,
+	    sc->sc_txfifosz, at91_getaddr, &atsc->tx_paddr, 0) != 0)
+		goto errout;
 
 	if (atsc->flags & HAS_TIMEOUT) {
 		/*
@@ -547,29 +551,22 @@ errout:
 static int
 at91_usart_bus_transmit(struct uart_softc *sc)
 {
-	bus_addr_t addr;
 	struct at91_usart_softc *atsc;
 	int err;
 
 	err = 0;
 	atsc = (struct at91_usart_softc *)sc;
 	uart_lock(sc->sc_hwmtx);
-	if (bus_dmamap_load(atsc->tx_tag, atsc->tx_map, sc->sc_txbuf,
-	    sc->sc_txdatasz, at91_getaddr, &addr, 0) != 0) {
-		err = EAGAIN;
-		goto errout;
-	}
 	bus_dmamap_sync(atsc->tx_tag, atsc->tx_map, BUS_DMASYNC_PREWRITE);
 	sc->sc_txbusy = 1;
 	/*
 	 * Setup the PDC to transfer the data and interrupt us when it
 	 * is done.  We've already requested the interrupt.
 	 */
-	WR4(&sc->sc_bas, PDC_TPR, addr);
+	WR4(&sc->sc_bas, PDC_TPR, atsc->tx_paddr);
 	WR4(&sc->sc_bas, PDC_TCR, sc->sc_txdatasz);
 	WR4(&sc->sc_bas, PDC_PTCR, PDC_PTCR_TXTEN);
 	WR4(&sc->sc_bas, USART_IER, USART_CSR_ENDTX);
-errout:
 	uart_unlock(sc->sc_hwmtx);
 	return (err);
 }
@@ -666,7 +663,6 @@ at91_usart_bus_ipend(struct uart_softc *sc)
 	if (csr & USART_CSR_ENDTX) {
 		bus_dmamap_sync(atsc->tx_tag, atsc->tx_map,
 		    BUS_DMASYNC_POSTWRITE);
-		bus_dmamap_unload(atsc->tx_tag, atsc->tx_map);
 	}
 	if (csr & (USART_CSR_TXRDY | USART_CSR_ENDTX)) {
 		if (sc->sc_txbusy)